Structure of two blue dyes obtained from the antimalarial drug primaquine were investigated. N-Acylprimaquines are photooxidized in chloroform solution to diquinolyl methines present in solution as imine salts. This blue dye was correlated by reduction with N-acetyl-methylenebisprimaquine, a microbial metabolite. The second blue dye is conveniently prepared from 5- hydroxdemethylprimaquine by photooxidation in sunlight and obtained in 50% yield. Its hydrogen bonded o-quinone structure was established on the basis of spectral data and by chemical reactions. Photooxidation of N-acylprimaquines dispersed on silica gel afforded o-quinones which were isolated and characterized. Antimalarial screening of these oxidation products of primaquine has been initiated. Optical isomers of primaquine prepared by published procedures did not show significant differences in an in vitro screening measuring tissue schizontocidal activity.